I have been listening to the HD800 through Audirvana via Schiit Eitr to Modi multibit connected to Jotunheim balanced. I thought this combo made the HD800 sound decent, not extraordinary by any means. OK soundstage and instrument separation, anemic bass, and above all, sibilance (Mimby works much better with my other tube amp, La Fiagro 339). I recently acquired a Chord Mojo and it significantly improved things with Jotunheim in all quarters, except sibilance. This was using the USB input of Mojo.
Next, I switched to the coax input of Mojo and connected through the Eitr. I have never heard a more dramatic improvement in a headphone from the same audio chain, just by adding one extra component (i.e. the Eitr). The sound became so much out of head with holographic and deep soundstage and amazing instrument separation. The soundstage moved more towards the front of the head becoming centrally situated, while before it was more towards the back. However, the most dramatic improvement was the complete lack of treble harshness and the sibilance was gone, (I am using the SDR mod) even from the 60s/70s albums that were unheardable through the HD800 before. I don't know how this happened, but it was magical. The HD800 now sounds smooth and extremely musical even with old recordings and sounds just effortless. Since the sound is so much out of the head with no treble glare, there is no fatigue and everything sounds really natural. The whole experience is almost to the point of being addictive. The only thing that I think comes a little short is a slightly less treble extension. In some of the classical albums, I think Mimby did slightly better with treble definition and texture, but everything else is really good, including the sense of space in live concert recordings and improved bass quantity. The bass is not light at all, just adequate even for EDM and hip hop (I listened to a few).
While I have never heard one of the very high end amps that do real justice to the HD800, I think, my current setup at the least gives a flavor of what those high end amps are capable of with the HD800. The sound quality has reached a level where I can easily imagine this to be my end game setup for quite some time. What is your experience if you have tried the same setup?